Gas chromatography (GC) is one of the valuable techniques of analytical chemistry for analysis of complex samples for both environmental and medical applications.
As a practical matter, a gas chromatograph is an analytical instrument that separates a gaseous sample, or a liquid sample which has been converted to a gaseous state, into individual compounds so that these individual compounds can be readily identified and quantified. A typical gas chromatograph includes an injector, an analytical separation column, a detector, and an output for displaying the results of the analysis.
The injector functions to convert samples to a gaseous state if needed, and moves the gaseous sample to the head of the analytical separation column in a narrow band. The separation column is typically a long coiled tube or the like, that separates the sample into its individual components. Separation columns typically contain liquid or solid materials as a stationary phase, and separate the individual components based on their affinity for the medium, i.e. polar compounds have an affinity for a polar medium and non-polar compounds have an affinity for a non-polar medium, and their molecular weights as they are swept through the column with a carrier gas. Typically, the larger the molecule, the longer it is immobilized within the solid or liquid material within the column, and the longer it is retained within the column.
The detector then detects and measures the constituent components as they emerge from the analytical column. Different sample components are retained for different lengths of time within the column, and arrive at the detector at characteristic times. These “retention times” are used to identify the particular sample components, and are a function of the type and amount of sorbtive material in the column, the column length and diameter, the carrier gas type and flow rate, and of the column temperature. Temperature control is a factor in obtaining repeatable data.
The output displays the results of the analysis to the user.
Gas chromatography is one of the most widely used and accurate methods for chemical identification. However, typical gas chromatographs which are employed in the laboratory are dimensionally large, heavy and not easily transported for use in the field.
In recent years, the interest in having portable, lightweight gas chromatographs capable of accurately detecting low and mid-levels of chemical agents has increased significantly. For example, there is a high interest in the use of such detectors to detect chemicals which may be used in warfare or for terroristic activities.
There remains a need in the art for an improved, lightweight, portable gas chromatograph which can accurately detect and transmit to a user, low to mid-level concentrations of chemical and/or biological agents.
In some embodiments, a gas chromatograph may use a thermal conductivity detector to detect and measure the constituent components of the gasses being analyzed. Thermal conductivity detectors utilizing thermistors are generally known in the art. Such thermistors are generally extremely small and fragile, and therefore the use of thermal conductivity detectors has typically been limited to fixed instruments that are kept in a very stable laboratory environment. There remains a need for a rugged thermal conductivity detector capable of withstanding the vibrations and temperature variations associated with use in the field.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.